1. Technical Field
Aspects of the present invention relate to a sheet conveyer device having a pair of discharge rollers, which nip a sheet therebetween and rotate to discharge the sheet out of a conveyer path, and an image forming apparatus having the sheet conveyer device.
2. Related Art
When an instruction for forming an image on a recording sheet is entered in an image forming apparatus (e.g., an inkjet printer), a feeder roller being pressed onto a surface of the recording sheet, which is stored in a sheet feed tray, rotates to direct the sheet into the sheet conveyer path. Along the sheet conveyer path in the image forming apparatus, several components for forming images are installed. Specifically, recording heads to record images on the recording sheet, a pair of conveyer rollers, and a pair of discharge rollers are provided. The conveyer rollers are arranged on an upstream side in the sheet conveyer path with respect to the recording heads, whilst the discharge rollers are arranged on a downstream side. The pair of conveyer rollers includes a driving roller, which is rotated by driving force provided by a drive source (e.g., a motor), and a subsidiary roller, which is pressed onto the driving motor and rotated according to the rotation of the driving roller. Similarly, the pair of discharge rollers includes a driving roller and a subsidiary roller. The driving rollers of the conveyer roller pair and the discharge roller pair are often connected to a single drive source and rotated in synchronization with each other. The recording sheet is carried in the sheet conveyer path by rotation of at least one of the conveyer roller pair and the discharge roller pair. The recording heads eject inks onto the surface of the recording sheet whilst the recording sheet is carried in the sheet conveyer path.
Japanese Patent Provisional Publication No. H09-58912 discloses a sheet discharging device for an image forming apparatus as above. The sheet discharging device specifically has a sheet sweeping rotary body, which is, according to the publication, a flexible and resilient piece (e.g., sponge) formed to have a shape of a gear. The sheet sweeping rotary body is attached onto a shaft of the driving roller of the discharge roller pair through an intervening one-way clutch. When the discharge rollers rotate in a direction to discharge the recording sheet into a discharge tray, the sheet sweeping rotary body rotates in the same discharging direction along with the driving roller of the discharge roller pair. When the sheet sweeping rotary body rotates, teeth in the gear can catch a rear end of the recording sheet so that the recording sheet is forwarded and swept out of the discharge rollers. When the discharge rollers rotate in a reverse direction which is opposite from the discharging direction, on the other hand, the sheet sweeping rotary body is not rotated due to an effect of the one-way clutch. Therefore, the recording sheet once discharged in the discharge tray is securely stopped by the discharge rollers from being reversely retracted once again between the discharge rollers, and reverse conveyance to convey the recording sheet in the reverse direction can be prevented.
Meanwhile, in the image forming apparatus, skew orientation of the recording sheet with respect to the conveyer path can be straightened by an operation so called a reverse registering operation. That is, when a feeder roller performs a feeding operation to pick up and feed the recording sheet into the sheet conveyer path, the conveyer rollers and the discharge rollers are rotated in the reverse directions so that the recording sheet conveyed to the conveyer roller pair is pushed back by the reverse rotation of the conveyer roller pair toward the upstream side of the sheet conveyer path. Thus, a front end of the recording sheet is halted at the conveyer roller pair and straightened with respect to the sheet conveyer path.